Strange Idle Behaviour

[pidj]

This being my first Porsche I would defer to you experienced owners. I have a strange idle behaviour once the vehicle warms up to operating temp: At stop, it drops to ~600 then bumps up to ~750 .... rarely it will kick up to ~1100 each time it returns to ~750. I have heard the MAF sensor mentioned in multiple posts dealing with multiple issues, but I don't know if this would be one of them. There is no smoke, no other symptoms. I use ethanol free Shell V Power petrol and STP Octane boost .... 2001 S .... everything stock.
I appreciate any thoughts on what this might be and the best was to troubleshoot.

Thanks!